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kottke.org posts about quantum mechanics

A visual explanation of quantum mechanics

posted by Jason Kottke   Jul 27, 2017

From the ViaScience YouTube channel comes this 31-part video explainer of quantum mechanics. As the introduction video notes, there is a fair bit of math in these videos presented at a quick pace, but if you took calculus in high school or college and remember the notation, that (and the pause button) should get you through this pretty well. (via @jsonpaul, who calls the series “fantastic”)

Quantum entanglement effects observed over 100s of miles

posted by Jason Kottke   Jun 19, 2017

A group of Chinese scientists say they have demonstrated the effects of quantum entanglement over a distance of 1200 km (745 miles).

Entanglement involves putting objects in the peculiar limbo of quantum superposition, in which an object’s quantum properties occupy multiple states at once: like Schrodinger’s cat, dead and alive at the same time. Then those quantum states are shared among multiple objects. Physicists have entangled particles such as electrons and photons, as well as larger objects such as superconducting electric circuits.

Theoretically, even if entangled objects are separated, their precarious quantum states should remain linked until one of them is measured or disturbed. That measurement instantly determines the state of the other object, no matter how far away. The idea is so counterintuitive that Albert Einstein mocked it as “spooky action at a distance.”

What’s weird to me is that all the articles I read about this touted that this happened in space, that an ultra-secure communications network was possible, or that we could build a quantum computer in space. Instantaneous communication over a distance of hundreds of miles is barely mentioned. Right now, it takes about 42 minutes for a round-trip communication between the Earth and Mars (and ~84 minutes for Jupiter). What if, when humans decide to settle on Mars, we could send a trillion trillion quantum entangled particles along with the homesteaders that could then be used to communicate in real time with people on Earth? I mean, how amazing would that be?

Update: Well, the simple reason why these articles don’t mention instantaneous communication at distance is that you can’t do it, even with quantum entanglement.

This is one of the most confusing things about quantum physics: entanglement can be used to gain information about a component of a system when you know the full state and make a measurement of the other component(s), but not to create-and-send information from one part of an entangled system to the other. As clever of an idea as this is, Olivier, there’s still no faster-than-light communication.

(thx, everyone)

Study: quantum entanglement is real

posted by Jason Kottke   Oct 22, 2015

The scientists who conducted a study at the Delft University of Technology in the Netherlands say they have proved that quantum entanglement is a real effect.

The Delft researchers were able to entangle two electrons separated by a distance of 1.3 kilometers, slightly less than a mile, and then share information between them. Physicists use the term “entanglement” to refer to pairs of particles that are generated in such a way that they cannot be described independently. The scientists placed two diamonds on opposite sides of the Delft University campus, 1.3 kilometers apart.

Each diamond contained a tiny trap for single electrons, which have a magnetic property called a “spin.” Pulses of microwave and laser energy are then used to entangle and measure the “spin” of the electrons.

The distance — with detectors set on opposite sides of the campus — ensured that information could not be exchanged by conventional means within the time it takes to do the measurement.

The study, published in Nature, has yet to be verified, but still, exciting!

Everything is made from something

posted by Jason Kottke   Aug 21, 2015

In A Children’s Picture-book Introduction to Quantum Field Theory, Brian Skinner explains quantum field theory — “the deepest and most intimidating set of ideas in graduate-level theoretical physics” — as if you and I are five-year-old children.

The first step in creating a picture of a field is deciding how to imagine what the field is made of. Keep in mind, of course, that the following picture is mostly just an artistic device. The real fundamental fields of nature aren’t really made of physical things (as far as we can tell); physical things are made of them. But, as is common in science, the analogy is surprisingly instructive.

So let’s imagine, to start with, a ball at the end of a spring.

(via @robinsloan)

Quantum mechanics made relatively simple

posted by Jason Kottke   Nov 13, 2013

Hans Bethe was a giant in the field of nuclear physics. He rubbed shoulders with Einstein, Bohr, and Pauli, was head of the Theoretical Division of the US atomic bomb project, and was awarded a Nobel Prize. In 1999, at the age of 93, Bethe gave a series of three lectures to the residents of his retirement community near Cornell University, where he had taught since 1935. Video of the lectures is available on the Cornell website.

In the first lecture, Bethe covers the development of the “old quantum theory”, covering the work of Max Planck and Niels Bohr. In the second and third lectures, he relates how modern quantum mechanics was developed, with a healthy amount of personal recollection along the way:

Professor Bethe offers personal anecdotes about many of the famous names commonly associated with quantum physics, including Bohr, Heisenberg, Born, Pauli, de Broglie, Schrödinger, and Dirac.

Without a doubt, this is the most high-power presentation ever made at a retirement home. (via @stevenstrogatz)

Is Google’s quantum computer even quantum?

posted by Jason Kottke   Nov 12, 2013

Google and NASA recently bought a D-Wave quantum computer. But according to a piece by Sophie Bushwick published on the Physics Buzz Blog, there isn’t scientific consensus on whether the computer is actually using quantum effects to calculate.

In theory, quantum computers can perform calculations far faster than their classical counterparts to solve incredibly complex problems. They do this by storing information in quantum bits, or qubits.

At any given moment, each of a classical computer’s bits can only be in an “on” or an “off” state. They exist inside conventional electronic circuits, which follow the 19th-century rules of classical physics. A qubit, on the other hand, can be created with an electron, or inside a superconducting loop. Obeying the counterintuitive logic of quantum mechanics, a qubit can act as if it’s “on” and “off” simultaneously. It can also become tightly linked to the state of its fellow qubits, a situation called entanglement. These are two of the unusual properties that enable quantum computers to test multiple solutions at the same time.

But in practice, a physical quantum computer is incredibly difficult to run. Entanglement is delicate, and very easily disrupted by outside influences. Add more qubits to increase the device’s calculating power, and it becomes more difficult to maintain entanglement.

(via fine structure)

Google’s new quantum computer

posted by Jason Kottke   Oct 16, 2013

Google’s got themselves a quantum computer (they’re sharing it with NASA) and they made a little video about it:

I’m sure that Hartmut is a smart guy and all, but he’s got a promising career as an Arnold Schwarzenegger impersonator hanging out there if the whole Google thing doesn’t work out.

Wipeout track using quantum levitation

posted by Jason Kottke   Jan 03, 2012

The quantum levitation videos I showed you a couple months ago are pretty cool, but scientists scienticiens at the Japan Institute of Science and Technology have upped the game by using QL CGI to build a real-world Wipeout track.

Say it with me: science!! Also, do Rainbow Road next! (via ★interesting)

Update: Say it with me: advertising! Or some other such nonsense. Several people have alerted me that this video is a fake…you can see vapor trails passing through walls, etc. Boo. Boo-urns. (thx, all)

Quantum levitation!

posted by Jason Kottke   Oct 18, 2011

What the what? This video gives a little more explanation into the effect at work here (superconductivity + quantum trapping of the magnetic field in quantum flux tubes) and an awesome demonstration of a crude rail system. You can almost hear your tiny mind explode when the “train” goes upside-down.

Wingardium Leviosa! (via stellar)

DNA and quantum entanglement

posted by Jason Kottke   Jul 16, 2010

Does quantum entanglement hold DNA together? Some physicists say it’s possible.

Rieper and co ask what happens to these oscillations, or phonons as physicists call them, when the base pairs are stacked in a double helix.

Phonons are quantum objects, meaning they can exist in a superposition of states and become entangled, just like other quantum objects.

To start with, Rieper and co imagine the helix without any effect from outside heat. “Clearly the chain of coupled harmonic oscillators is entangled at zero temperature,” they say. They then go on to show that the entanglement can also exist at room temperature.

That’s possible because phonons have a wavelength which is similar in size to a DNA helix and this allows standing waves to form, a phenomenon known as phonon trapping. When this happens, the phonons cannot easily escape. A similar kind of phonon trapping is known to cause problems in silicon structures of the same size.

Quantum mechanics just got REAL

posted by Jason Kottke   Mar 18, 2010

The opening paragraph of the article says it all:

A team of scientists has succeeded in putting an object large enough to be visible to the naked eye into a mixed quantum state of moving and not moving.

Wait, what? Like, WHAT? Ok, let’s start over:

Andrew Cleland at the University of California, Santa Barbara, and his team cooled a tiny metal paddle until it reached its quantum mechanical ‘ground state’ — the lowest-energy state permitted by quantum mechanics. They then used the weird rules of quantum mechanics to simultaneously set the paddle moving while leaving it standing still.

The fuck? In my day, we were taught, with the help of non-graphing calculators and paper notebooks, that quantum mechanics was a lot of wand-wavey nonsense about wave/particle duality that you never had to worry about because it belonged to some magical tiny land that no one visits with their actual eyes. This…this is straight-up magic. [Cue Final Countdown]

Nature’s quantum computers

posted by Jason Kottke   Feb 11, 2010

One of the big bummers about quantum computing is the cold temperatures required (hundreds of degrees below zero). However, a number of researchers believe that certain algae and bacteria perform quantum calculations at room temperature.

The evidence comes from a study of how energy travels across the light-harvesting molecules involved in photosynthesis. The work has culminated this week in the extraordinary announcement that these molecules in a marine alga may exploit quantum processes at room temperature to transfer energy without loss. Physicists had previously ruled out quantum processes, arguing that they could not persist for long enough at such temperatures to achieve anything useful.

(via mr)

The unobserved tree makes noise

posted by Jason Kottke   Mar 09, 2009

Two independent groups of scientists have recently confirmed that the universe does exist when we are not observing it.

The reality in question — admittedly rather a small part of the universe — was the polarisation of pairs of photons, the particles of which light is made. The state of one of these photons was inextricably linked with that of the other through a process known as quantum entanglement. The polarised photons were able to take the place of the particle and the antiparticle in Dr Hardy’s thought experiment because they obey the same quantum-mechanical rules. Dr Yokota (and also Drs Lundeen and Steinberg) managed to observe them without looking, as it were, by not gathering enough information from any one interaction to draw a conclusion, and then pooling these partial results so that the total became meaningful.

That’s a relief, although the head of one of the group called their results “preposterous”, so perhaps we’re still not really here.

Faster-than-light communication

posted by Jason Kottke   Aug 18, 2008

In a Swiss experiment, two entangled photons 18 km away from each other were able to communicate with each other almost instantaneously.

On the basis of their measurements, the team concluded that if the photons had communicated, they must have done so at least 100,000 times faster than the speed of light — something nearly all physicists thought would be impossible. In other words, these photons cannot know about each other through any sort of normal exchange of information.

Update: Hrm, the link above scampered behind Nature’s paywall. Here’s a post on the Scientific American blog instead.

Physicists at the University of Washington are

posted by Jason Kottke   Nov 17, 2006

Physicists at the University of Washington are hoping to use entangled photons to send information back in time. “Here’s where it gets weird.”

Researching quantum honeybees

posted by Jason Kottke   Jun 14, 2005

Researching quantum honeybees. Can bees detect quantum fields and use them to find food?

Brian Greene on Albert Einstein’s miracle year,

posted by Jason Kottke   Apr 08, 2005

Brian Greene on Albert Einstein’s miracle year, his discovery of the photoelectric effect, and his uneasiness with quantum mechanics.